GENERAL: Garmin
claims you can create Custom Maps in five easy steps (HERE).
'Your mileage may differ,' but using Google Earth to create Custom Maps
was a time-consuming pain for this reviewer. For the serious hiker,
it seems that the USGS 1:24,000 DRG topo maps would be the most useful
and legible on the GPS screens. Google Earth isn't especially helpful
in converting these maps to the required .kmz maps needed for the Garmin
units.

Eventually I came across Global Mapper (about
$300) which among its many features is an ability to import georeferenced
DRG .tif or Google Earth .jpg files and export them as a series of 100
or less georeferenced .kmz map files.

PROGRAM SETUP:Exporting the data files as .kmz files to
the Garmin unit is easy as 1, 2, 3, 4.

Click on these
thumbnails for larger views..........Open DRG Files
°
Open Control Center
Open GPS Tab

1. Open as many DRG geo-referenced .tif
files as you like with Ctrl-O. Notice, however that the borders are
visible and overlap on each other.2. Open the Overlay Control Center:
Tools, "Control Center..." or (Alt-C), and highlight all the DRG
maps you want to trim off the borders.

The program should find the unit's \Garmin\CustomMaps
folder and automatically save 96-100 Cells (maps) to the GPS. (Remember
the GPS unit has a limit of 100 maps per Custom Map). Also, the Basemap
(which is required to be active in order to see your tracks) will not display
the inaccurate Basemap highways.

CAUTION:Always wait for the progress bars to completely
disappear before unplugging the unit. There is a delay from
the time the bars show "complete" to when the .kmz files have actually
been created and transferred to the unit.

CONCERNING IMAGE
QUALITY:In the Garmin Raster Export tab (above) is
a place to adjust the "Image Quality". This actually only adjusts
the exported .jpg compression before the maps are converted into .kmz files.
I experimented with various Image Quality selections, and discovered that
one could reduce the "Quality" to 10% without any discernible decrease
in map resolution on the GPS screens. Using a 10% Quality factor
results in .kmz files that are about 1/3rd the size as when using the Default
value of 50%. This can reduce computer time significantly.

The Basemeap Problem:In the Dakota, one must make the Basemap "Enabled"
in order to see tracks. Manually determining the number of cells
per DRG will not hide the Basemap highways. One must use the "GPS"
method (described above) which incorporates a Draw Order to hide the basemap,

CREATE
CONTOUR LINES FROM DEM DATA:DEM data are nothing more than elevation points
in the US and around the world. The points in US are in grids with
10m or 30m squares. It's up to outside programs (like Global Mapper
or Garmin/Magellan maps) to compute the contour lines and add terrain and
other features. In the case of Global Mapper, the DEM data is stored
on their own servers for faster downloads.

1. File, US Data, Highlight: Download
Online Imagery/Topo/Terrain, US Elevation Data (10m resolution).2. Pre-determine the location central
point of your area of interest.3. Check: "Within".4. Specify the radius (1 to 2 miles)
and Lat/Long of the central point in the hddd.ddddd format, OK. (A relief map of your area should
download and appear).

Check Thumbnails
for Full Views........

5. In the Shader dropdown box,
you may want to choose Atlas rather than Color Ramp.6. You can save this area of work
with Ctrl-S.7. File, Generate Contours, elect
Contour Interval, (usually 10', 20', or 50') OK. (Contour lines should
appear on the relief map.)8. Activate the Overlay Control
Panel with Alt-C.9. Uncheck the US Elevation Data,
and highlight the GENERATED CONTOURS.10. Select: Options, Line Styles, check: Assign
Random Colors to Features. (In Select Line Style,
you should use a width of 1, 2, or 3 pixels depending on the roughness
of the terrain), OK, OK.11. The contour lines should now have random
colors.12. File, Export Vector Format.13. In Select Export Format, choose KML/KMZ,
check Display Labels for Area and Line Features, OK.14. Give the exported .kmz file a logical
name.15. Clicking the resulting .kmz file should
make it appear on Google Earth with some elevations labeled.

The .kmz file will superimpose the contour
lines on Google Earth -such as (HERE).
To identify an unknown contour in Google Earth, click on it and a box will
show the elevation.

Working with Garmin
Custom Maps:After generating and coloring contours in
11. above:12. GPS, Send Raster Maps to Garmin
Connected Device, OK.13. Give the exported .kmz file a name.14. This file can be uploaded to Garmin
units that support Custom Maps.

NOTE: There is a practical limit to the size
the Garmin Custom Maps can handle without the contours smearing and losing
resolution. This occurs with maps downloaded with greater than 2
to 3 mile radiuses from the central point, creating files greater than
about 2 MB.

But these files will have 33 or less tiles
allowing three, four, or five .kmz maps to be displayed on the unit at
the same time and stay within the 100-tile Custom Map limit. One
can determine the number of tiles by changing the .kmz file to a .zip file
which will show the number of tiles.

Alternate
Method for Large Maps:After generating and coloring contours in
11. (above) with radiuses of 4 miles or greater. (The upper limit
is unknown at this time).12. GPS, Send Raster Maps to Garmin
Connected Device.

Thumbnail
4.5 Mile Radius

...

13. In Garmin Raster Export Options,
click on "Click Here to Calculate Spacing in Other Units."14. Select 'Units', 'meters'.
Enter "2.4" (DRG standard) for 'X/Longitude Spacing', OK, OK. (The
correct Y/Latitude value will then be calculated).15. Give the exported .kmz file a name.
The file will have 99 tiles.16. Only one file of this size can be
uploaded to Garmin units that support Custom Maps, but it will have high-resolution
contours.

EXTRACT
CONTOUR LINES from GeoPDF Topo Maps (v. 13 required):The new GeoPDF Topo Maps can be downloaded
free from (HERE).
These
maps are similar to the USGS topo quadrangle maps and have the same names.
However, they contain 'layers' of geographical features that can be viewed
separately. At present Global Mapper is the only program we know
of that can extract individual features and display them on Google Earth.

Google Earth aerial photos can not show contour
lines, although their images can be viewed in 3-D. Global Mapper
v. 13 can extract the contour lines as a .kmz file, which can then be displayed
on Google Earth. The procedure is as follows:

2. In: Select Layers to Render, uncheck all but
Contour Features and Contour Names, OK. (The contour lines will be displayed
with a white background.)3. In the Overlay Control Panel (Alt-C), Options,
Raster Options, check 'Transparent', and select Set Transparent Color. (Click the white box, OK.
Now the map will have no white background.)4. In File, Export Raster/Image Format, in
Select Export Format, select KML/KMZ, OK.5 In KML/KMZ Export Options, select
'PNG (supports Transparency)'. If this isn't checked, the 'white
paper' will override the GE terrain maps.6. In the Save As dialog box, give the map
a logical name, and save.

A .kmz file will be created in the folder with
the GeoPDF file which when clicked on, will superimpose the contour lines
on Google Earth -such as (HERE)..

DATUM:Most DRG maps are in the NAD-27 datum.
However, some of the later maps are in the NAD-83 datum. And even though
some of these are georeferenced incorrectly to NAD-27, Global Mapper corrects
this automatically.

As with ANY map, to avoid UTM Northing errors
of approximately 200 meters in the GPS unit, the Position Format should
be set to the datum of the map being displayed. Lat/Long errors from
an incorrect datum are in the range of the GPS errors and are therefore
negligible.